Plastics such as polyesters are typically produced from petrochemical sources by well-known synthetic means. These petrochemical-based polymers can take centuries to degrade after disposal. Concern over plastic waste accumulation in the environment has resulted in a recent movement toward using biodegradable polymers instead.
Bio-based biodegradable polymers, also commonly referred to as “bioplastics,” have not enjoyed great success in the marketplace due to their high production cost. However, advances in biotechnology have led to less expensive methods for their production. In one instance, biodegradable aliphatic copolyesters are now often produced by large-scale bacterial fermentation. Collectively termed polyhydroxyalkanoates, also known as “PHAs”, these polymers can be synthesized from plant or bacteria fed with a particular substrate, such as glucose, in a fermentation plant. In many instances, the structural or mechanical properties of PHAs can be customized to fit the specifications of the desired end product. PHAs can degrade both aerobically and anaerobically.
PHAs are enormously versatile, and as many as 100 different PHA structures have been identified. PHA structures can vary in two ways. First, PHAs can vary according to the structure of the pendant groups, which are typically attached to a carbon atom having (D)-stereochemistry. The pendant groups form the side chain of hydroxyalkanoic acid not contributing to the PHA carbon backbone. Second, PHAs can vary according to the number and types of units from which they are derived. For example, PHAs can be homopolymers, copolymers, terpolymers, or higher combinations of monomers. These variations in PHA structure can cause variations in their physical characteristics. These physical characteristics allow PHAs to be used for a number of products that may be commercially valuable.
PHAs can be processed to produce articles for consumer use. Thermoplastic polymers including PHA can be transformed into articles for consumer use by first melting the polymer, shaping the molten polymer, and finally solidifying the polymer, normally by crystallization. Accordingly, crystallization rate is an important parameter that can control the rate of processing of PHA polymers. As a general rule, the faster the PHA can be crystallized, the faster the polymer can be processed. In addition, certain polymer forming processes including film blowing and melt fiber spinning may be difficult to perform in a practical manner if the crystallization does not occur fast enough. In these cases, the molten polymer is shaped in a way that is stable only over a short period of time. If crystallization does not occur within the necessary time frame, the process can be unsuccessful. Therefore, in some cases, the speed of crystallization weighs heavily on whether certain polymer processes are practical.
The patent application JP 07 188537 A (TOKUYAMA SODA KK) discloses a copolymer of hydroxybutyrate and hydroxyvalerate. Hydroxyvalerate is a HA unit which has only 5 carbon atoms. To raise the crystallization rate of the copolymer, this document discloses the addition of a fatty acid system compound chosen from fatty acid, fatty acid ester, fatty acid amine and fatty acid metal salt.
Therefore, there is a need for rapid processes and reagents that are useful for crystallizing PHA polymers. Such processes and reagents can be efficient, cost-saving, and suitable to large-scale processing of PHA materials.